Marine Creatures of the Northern Gulf of Mexico – Green Algae

With this article we will shift from the microscopic creatures of the Gulf of Mexico to the macroscopic ones – ones you can see without a microscope.  We will begin with the simplest and most primitive of macroscopic creatures – the seaweeds.

Many locals see the grass washed ashore along the Intracoastal Waterway and call this seaweed, but it is in fact seagrass.  Seaweed differs from seagrass in that they are not true plants. True plants are vascular – meaning they have a series of “veins” running through their body called xylem and phloem.  These veins move water and material throughout the body – similar to the arteries and veins of an animal.  But seaweeds lack this “circulatory” system, rather they absorb water through their tissues and must live in the water environment to do this.  Seaweeds lack leaves, stems, and roots.  They do not produce seeds or flowers, but they do require sunlight and nutrients and conduct photosynthesis as true plants do.  When I was in college seaweed was considered simple plants – just nonvascular ones.  Today biologists believe they are too simple to be considered plants and thus are a group existing between the microscopic phytoplankton and the true vascular plants we know from our lawns and forests.  They are often called algae as well as seaweed.

Biologists divided the seaweeds into divisions based on their color, which is determined by the photosynthetic pigments they have for photosynthesis.  Compared to my college days, the classification of green algae is quite complex.  The entire group was once placed in the Division Chlorophyta.  Today, most sources consider only the marine forms of green algae in the group Chlorophyta, with numerous other groups consisting of thousands of species.  Most green algae live in freshwater and are believed to be the group that led to the land plants we are familiar with.  Their photosynthetic pigments include chlorophyll and a and b but also carotene and xanthophyll.  The pigments are dominated by the chlorophylls – hence their green color – and the ratio of chlorophyll to carotene and xanthophyll is the same as the plants you find in your yard – hence the argument they led to the evolution of land plants.

Green algae – or any of the seaweeds – are not as common along the northern Gulf of Mexico as you find on other coasts.  Not having true roots, stems, or leaves, seaweeds must attach themselves to the seafloor using a suction cup type structure called a holdfast.  To attach, the holdfast must have a rock of some type.  Along the rocky shores of Maine and California, they are quite common.  Even with the limestone rock of south Florida you can find these.  But the fine quartz sand of the northern Gulf of Mexico is not as inviting to them.  That said, we do find them here and most are found on man-made structures such as jetties, seawalls, and artificial reefs – I found one attached to a beer can.

Of all of the green algae that exist in Florida, I have only encountered three.  One is called “sea lettuce” in the genus Ulva.  Attached to rock jetties and seawalls, it looks just like lettuce and is beautiful, brilliant green in color.  It grows to about seven inches in height and is used as a food source in different countries.  It can become a problem if local waters are high in nutrients due to pollution from land sources.  It will grow abundantly, reducing habitat for other species, and wash ashore during storms where it breaks down releasing gases that can be toxic to shore life and humans.  I first encountered it growing on the rock jetties at St. Andrews State Park in Panama City, but it does grow on local hard structures.

“Dead Man’s Fingers” – Codium – is another green algae I first encountered it on the jetties of St. Andrews.  The thick finger-like projections of this seaweed extending from the rocks did resemble a glove – or the fingers of a dead man within the rocks.  Some species around the world are used for food.  But I could not find any references that it is here.

The third species of green algae I have seen locally is known as the “Mermaids Wine Glass” – Acetabularia. This beautiful seaweed is relatively small and does resemble a wine, or martini glass.  They are quite abundant in south Florida and is the one I found growing on a beer can submerged in Santa Rosa Sound.   

Though seaweeds in general are harder to find along the northern Gulf coast, they are fun to search for and do play a role as primary producers here.

 

 

References

Green Algae. Wikipedia. https://en.wikipedia.org/wiki/Green_algae.

Deadman’s Fingers. Monterey Bay Aquarium. https://www.montereybayaquarium.org/animals/animals-a-to-z/dead-mans-fingers.

Introduction to Green Algae. University of California/Berkley.  https://ucmp.berkeley.edu/greenalgae/greenalgae.html.

Ulva Lactuca. Wikipedia. https://en.wikipedia.org/wiki/Ulva_lactuca.